This week we have an article out in the American Journal of Physical Anthropology looking at reconstructing the lives of the St. John’s, Milton individuals using isotopic analysis. In this post we explain how we do this kind of analysis, and give you some of the highlights of the article.
In previous posts I’ve talked about how we can look at different isotopes of the chemical elements in your body to work out where people came from, or what they were eating – these are important things in understanding a person’s day to day life and really interesting to us as bioarchaeologists. The article that we’ve just published uses these techniques on small samples of bones, teeth and hair from the people of St. John’s Milton.
Why sample three different tissues from the same person?
It might seem a bit wasteful to take samples of lots of different parts of the body… but actually each of the tissues we’ve sampled forms at a different time in a person’s life. So each sample tells us a different bit of their lifestory.
Teeth start forming when you’re still in the womb (or at least some of them do) and keep forming through your early childhood. In fact teeth grow at a known rate, and if we take 1mm slices of a tooth we can look at slices of childhood life. In our study we’ve mostly looked at teeth that’ll give us a look at how a child was fed in very early life. For example, your first molars are forming from about when you’re 4 months old until about 9.5 years, and a 1mm slice of them will represent about 6-9 months of life (Beaumont & Montgomery, 2015 is the source of all knowledge on the timings of these). By taking lots of tiny slices we can reconstruct early life changes in diet in lots of detail. This means we can l look at things like infant feeding, weaning patterns, or childhood dietary change and sickness. We’ve written a bit more on that in our Little Lives series.
Your bones, on the other hand, start forming when you’re in the womb, but bone is being destroyed and formed all through your life (we call this remodelling). That means when we sample bone for isotopic analysis we’re not looking at bone that formed in the womb, but instead bone that has been remodelled much later. Our samples are sort of an average, that might take in the last 10 years of a person’s life (or much longer for some bones that remodel slowly). We use bone results as generally representing adult life.
Hair samples give us much more time resolution. As we all know, is growing all the time – in fact hair grows about 1cm per month (so that’s why my grey hairs have become so much more visible during lockdown!). If we have hair preserved we can cut it into 1cm pieces and look at what a person was eating on a month-by-month basis right up until time of death (the bit of hair closest to the scalp). It’s really rare that hair is preserved in archaeological sites, but when it is there it can tell us a lot.
Here’s a handy diagram that sums all this up:
Where did the Milton population come from?
We used isotopes of strontium from teeth to work out the areas the people of Milton may have come from. Strontium relates to the kinds of rocks people are living on as their teeth grow – more on that here, so it can give us possible areas of origin. Most of the Milton population came from the UK, and we compared their isotope values to places in the UK that should have similar values – this map shows the possible places that they might have come from in grey…
We know that one of our identified individuals – the town doctor – came from Germany though. He has really different strontium isotope values to the rest of the Milton people, and when we match them to possible places of origin in Germany there’s a really limited range of places he could have come from, all in Southern Germany.
What was their childhood outside of NZ like?
We can also see, looking at isotopes that relate to diet, that our Milton settlers seem to have all had fairly different childhood experiences while they were growing up. Some people seem to have been weaned very early (by 9 months old), other’s weren’t fully weaned until they were around 3.5 years old. These differences are probably because of the different social situations of their families.
In the 1800s urban mothers in the UK often had to return to work in the town’s factories quite quickly after giving birth – they needed that income to keep their family going and couldn’t afford to stop work for long. This might mean they couldn’t breastfeed new babies for as long as they might have liked to. Longer breastfeeding was more common in rural families, where mothers could stay near their children while they worked, and weaning later reduced their chances of getting pregnant again quickly and having another mouth to feed! Rich women, on the other hand, were often advised to wean their children early so that they could return to society and get pregnant again quickly to produce more heirs. In Milton it looks like our settlers had a mixture of backgrounds which led to big differences in how long they were breastfed for.
Once children were weaned our analysis can tell us about their childhood diet. Most people in the St John’s burial ground seem to have had a pretty consistent diet through childhood – based on farmed crops and animals. This consistent diet might mean that most of them came from towns where a variety of foods were available year round.
There is one exception to this – the doctor’s wife (another of our identifiable individuals). She seems to have been fed quite seasonally as a child, the isotope values in her teeth change relatively regularly – we think this reflects her rural Scottish upbringing. Country populations often didn’t have year round access to certain foods and had to change their diets as different foods became available or disappeared.
Moving to a ‘land of plenty’ – does their diet improve in NZ?
We then looked at how life changed with the move to New Zealand for the adult settlers of St. John’s Milton. Their teeth show us what was happening before they emigrated, and their bones/hair tell us about their lives in colonial New Zealand. We can see that most people’s diets change a little bit with the move to New Zealand. As we’ve talked about before, the plentiful meat that the New Zealand company advertised as being a part of colonial life isn’t that obvious in our analysis, but people don’t seem to have been any worse off than they were in the UK. Two people are exceptions to this (our town doctor and B29), who seem to have enjoyed quite meat-rich diets in New Zealand.
Signs of stress in the colony?
Isotopes can also tell us about periods of stress that people experienced. When bioarchaeologists say ‘stress’, we don’t mean anxiety or worry, but instead physiological stress – times when disease or starvation alters your body’s metabolism. Serious stuff! During these times your body starts eating its own fat stores to keep your energy levels up, and that changes the chemistry of your forming tissues.
Looking at the preserved hair from some of the Milton population shows that two people in the group potentially have these changes close to death. One of them we’ve already talked about – B21 who died of tuberculosis – the wasting this disease causes is a good candidate for changing the body’s chemistry. The other one (B23) is an unidentified individual that we don’t know very much about because their bone preservation was quite poor, but their raised isotopic ratios close to the end of life suggest that some kind of illness or starvation was being experienced.
An unusual individual…
In almost all aspects of our work B29 (an unknown female burial) stands out as being a bit unusual. She is the person who was weaned very early, she seems to have had high levels of meat intake both before moving to New Zealand and in the colony, and she has very fancy coffin decorations compared to the rest of the group… but she also has some interesting evidence in her bones for illness throughout life. We’re hoping to write more on her once our paleopathologists (Hallie and Annie) have looked at her in more detail, so stay tuned!
For people who are big fans of graphs, numbers, and academic-jargon the full article can be found here (if you have institutional access).
Charlotte King, 22nd May 2020
King CL, Buckley HR, Petchey P, Kinaston RL, Millard AR, Zech J, et al. 2020. A multi-isotope, multi-tissue study of colonial origins and diet in New Zealand. American Journal of Physical Anthropology. Early View.
Evans J, Montgomery J, Wildman G, Boulton N. 2010. Spatial variations in biosphere 87 Sr/ 86 Sr in Britain. Journal of the Geological Society London.167:1–4.